This invention relates to a circuit arrangement for supplying a direct current or a low-frequency commutated direct current to a lamp, comprising;
supply input terminals for connection to the poles of a supply voltage source supplying an alternating current, PA1 rectifier means coupled to the supply input terminals to rectify the alternating current and provided with a first output terminal and a second output terminal, PA1 a buffer capacitance coupled to the output terminals of the rectifier means, PA1 a DC-DC converter of the downconverter type coupled to the buffer capacitance and provided with PA1 a third chain which comprises a second circuit element and which shunts the first unidirectional element, PA1 a second control circuit which is coupled to a control electrode of the second circuit element and which serves to render the second circuit element high-frequency conducting and non-conducting at the frequency f1, and PA1 a fourth chain which shunts the first circuit element and which comprises a series arrangement of a second capacitance and a second unidirectional element, a junction point of the second capacitance and the second unidirectional element being coupled to the first output terminal of the rectifier means. PA1 a fifth chain which comprises a series arrangement of a third capacitance and a third unidirectional element and which shunts the second circuit element, PA1 a sixth chain which comprises a series arrangement of the first inductive element and a fourth capacitance and which shunts the first circuit element, PA1 a seventh chain which comprises a fourth unidirectional element and which shunts the first circuit element, and PA1 a circuit part COM which is coupled to the first and the second control circuit for the low-frequency commutation of the direct current at a frequency f0, f0 being smaller than f1.
a first chain which interconnects the output terminals and comprises a series-arrangement of a first circuit element and a first unidirectional element, PA2 a first control circuit coupled to the first circuit element to render the first circuit element high-frequency conducting and non-conducting at a frequency f1, and PA2 a second chain which shunts the first unidirectional element and comprises a series arrangement of a first inductive element and a first capacitance.
Such a circuit arrangement is well-known. The known circuit arrangement can very suitably be used for supplying a direct current to, for example, a high-pressure discharge lamp. A disadvantage of the known circuit arrangement, however, resides in the fact that current is taken from the supply voltage source almost exclusively when the amplitude of the supply voltage is high. As a result, the power factor of the known circuit arrangement is low.